Butterfly valves generally consist of a valve housing and a rotatable disc sealably disposed within the housing. Standard coupling means connect the valve to adjacent tubes and pipes.
The rotatable disc is pivotally mounted within the housing to project a perpendicular face to the direction of fluid flow in order to close the valve. Conversely, the valve is fully opened by rotating the disc in a plane essentially parellel to the fluid flow. Infinite gradation of "openness" and "closedness" are permissible.
Butterfly valves may be found with metal discs tightly seating against the metal interior of the valve body as well as with various combinations of polymeric coated components within the interior of the valve. Representative designs of the latter types may be found in U.S. Pats. No. 3,750,698; 3,958,595; 3,753,549; 3,804,366; and 2,809,060.
A dificulty encountered with available butterfly valves is when they are used to control flowing sandfill in underground excavations. After an area is opened or mined out, it is usually supported or closed up in some fashion to reduce the number of dangerous voids in the mine. One such technique is introduce cementious fill into the void. Sandfill, comprised essentially of small erosive sand particles suspended in a water slurry, is piped to the desired location. Sandfill moving at pumped velocities easily abrades piping components. Valve structures, such as seats, discs, pivoting assemblies, the interior of the valve housing etc., are literally destroyed in short order. The valves fail when they begin to leak; refuse to open or close to the desired orientation; and eventually jam. In large excavation, the expense and effort needed to repair and ultimately replace the damaged valves becomes excessive. Downtime simply compounds the problem.
Currently available valve designs simply have not withstood the demands placed upon them.